Flexibility evaluation of wind-PV-hydro multi-energy complementary base considering the compensation ability of cascade hydropower stations.

• The flexibility evaluation method framework of the WMCB power system is proposed. • The LOFP, LOFE, and FDS indices are introduced to measure the flexibility margin of the WMCB. • The appropriate capacity ratio of the wind-PV power to hydropower in the WMCB should be 1:1 ∼ 1.5:1. The widespread expansion of renewable energy, like wind and photovoltaic (PV), increases the importance of power system flexibility. Quantify the balance between the flexibility supply of hydropower and the flexibility demand of wind-PV power is the key to the planning and development of multi-energy complementary system. Based on the power system flexibility balance principle, a novel flexibility evaluation method is proposed for watershed-type wind-PV-hydro multi-energy complementary bases (WMCB) considering the complementary characteristics of cascade hydropower stations. First, the wind and PV power capacity ratio are determined by complementarity index, and the timing production simulation model are used to determine the wind-PV-hydro power output to calculate the flexible supply. And the flexibility demand is calculated by the combined bias distribution of the wind-PV power output states. Then, the flexibility margin distribution is calculated by the convolution difference, and loss of flexibility probability (LOFP), loss of flexibility expectation (LOFE), and flexibility demand shortage (FDS) indices are used to measure various aspects of the WMCB system flexibility margin. Finally, the relationship is established between the wind-PV power capacity and system flexibility margin indices, and the impact of wind-PV power capacity improvement on the system flexibility margin is analyzed. To verify the feasibility of the method, the WMCB of the downstream Yalong River basin is taken as a case study, and 21 wind-PV power capacity scenarios are set as the comparative schemes. The case study results indicate that the wind and PV power capacity rate should be 0.43:0.57. The suitable wind-PV power developing capacity of the WMCB should be 12.7 GW to 14.7 GW without other flexibility resources. And the developing development potential of wind-PV power capacity would reach about 22.0 GW with 1600 MW upward flexibility resources and 850 MW downward flexibility resources. This study provides a novel method framework for the flexibility analysis of the wind-PV-hydro power systems and provides a valuable reference for the planning and design of WMCBs. [ABSTRACT FROM AUTHOR]